Intrauterine Position Research Articles

Ultrasound assessment of postplacental copper intrauterine device position 6 months after placement during cesarean delivery

ObjectiveThe objective was to describe the sonographic position of copper intrauterine devices (IUDs) 6 months after insertion during cesarean delivery. Study designThis prospective, observational study followed participants who received a copper IUD during cesarean delivery. We performed pelvic examination at 6 weeks and 6 months and sonography at 6 months to determine IUD position. Patients had additional examinations as needed to address complications. ResultsSixty-nine participants provided outcomes through 6 months: 41 (59%) had correctly positioned IUDs, 21 (30%) had malpositioned intrauterine IUDs, 5 experienced expulsion (3 partial, 2 complete), and 2 had elective removal; 52 (75%) had missing strings. Missing strings at 6 weeks predicted an incorrect IUD position in 22 of 52 participants (positive predictive value 42%), and visible or palpable strings predicted a correct IUD position in 7 of 12 participants (negative predictive value 58%). ConclusionAlthough 59% of copper IUDs placed during cesarean were correctly positioned at 6 months, nearly one third were malpositioned. ImplicationsUltrasound may be indicated for patients receiving a copper IUD during cesarean delivery as checking IUD strings alone does not assure correct placement. Providers offering postpartum IUDs should ensure that appropriate processes for the evaluation and management of devices with missing strings or abnormal position are available to all patients regardless of insurance status.

The influence of the levonorgestrel‐releasing intrauterine system position on bleeding patterns in reproductive age women

To determine whether users of the non-fundal levonorgestrel-releasing intrauterine system (LNG-IUS) present with unfavorable bleeding patterns more frequently than fundal LNG-IUS users. A prospective cohort was conducted from June, 2016 to January, 2018 involving women aged 18-45years who wished to use the LNG-IUS as contraception and had no contraindications, endometrial polyps, submucosal myomas, irregular menstrual cycle, or anticoagulant use. Two study groups comprised women using fundal insertion and non-fundal insertion LNG-IUS. Bleeding was evaluated using a diary and pictogram chart. Of the 92 women who participated in the study, those with non-fundal LNG-IUS insertion sustained bleeding at rates greater than 83% (31) in the first 3months of use, and 58% (14) at 6months, versus 51% (22) at 3months and 33% (19) at 6months in those with fundal insertion (P=0.002 at 3months; P=0.037 at 6months). Blood loss in the non-fundal LNG-IUS group was higher than in the fundal LNG-IUS group according to pictograms drawn by participants. Women with non-fundal LNG-IUS placement had a higher frequency of sustained bleeding and blood loss volume according to self-reported charts than those with fundal LNG-IUS placement.

Intrauterine position and adjacent fetal sex affects fetal and placental growth throughout gestation, but not embryonic viability, in pigs selected for component traits of litter size

Intrauterine position and sex of adjacent fetuses in litter bearing species have been implicated in physiological and behavioral differences of offspring. The effects of uterine position and sex status of flanking fetuses with crowded uterine conditions on fetal and placental growth rate was tested. Gilts were unilaterally hysterectomized-ovariectomized at 160 d of age and mated at approximately 280 d of age, with fetal harvest at 45, 65, 85, or 105 d of gestation. Uterine position relative to the cervix, fetal status (alive, dead, sex), fetal weight, and placental weight were recorded at harvest. Each fetus was coded as adjacent to 0, 1, or 2 opposite sex fetuses and analyzed using an ANOVA fitting contemporary group, line, and flanking fetal sex code as fixed effects with sire as a random effect. The fraction of live fetuses in each classification (0, 1, 2) was 26.4%, 50.1%, and 23.4%, respectively, indicating no effect on fetal survival. Fetal weight was affected by flanking sex status between 65 d (P < 0.05) and 105 d (P < 0.001), with means at 105 d of 800.0 ± 20.3, 748.5 ± 17.8, and 672.7 ± 25.2 g, respectively for flanking sex status codes 0, 1, 2. Placental weight was similarly affected (P < 0.01) by flanking sex code, but only at 105 d. It is concluded that fetal growth and placental development in pigs is influenced by sex status of adjacent fetuses. This could be a potential source of variation in behavioral and reproductive differences later in life.

Non-model species deliver a non-model result: Nutria female fetuses neighboring males in utero have lower testosterone

Neighboring fetuses may impact their siblings in various respects, depending on their in utero location and sex. The effects of the intrauterine position (IUP) are widely studied in model organisms, especially laboratory bred murine strains that are characterized by short gestations and altricial offspring. In some species, the proximity to a male fetus and its higher circulating testosterone masculinizes neighboring female fetuses. In utero testosterone exposure might be manifested as higher testosterone concentrations, which contribute to a variation in morphology, reproductive potential and behavior. In this study, we examined the influence of neighboring an opposite sex fetus on testosterone levels in a feral animal model characterized by a long gestation and precocious offspring. Using necropsies of culled nutria (Myocastor coypus), we accurately determined the IUP and quantified testosterone immunoreactivity in fetal hair. We found that as expected, both male and female fetuses neighboring a male in utero had longer anogenital distance. However, females adjacent to males in utero showed lower testosterone levels than male fetuses, while testosterone levels of females without a male neighbor did not differ from those of males. This surprising result suggests an alternative mode by which local exogenous steroids may modify the local fetal environment. Our study emphasizes the importance of examining known phenomena in species with different life histories, other than the traditional murine models, to enhance our understanding of the evolutionary mechanisms that are driving sexual differentiation.

Brachial Plexus Birth Injury in Elective Versus Emergent Caesarean Section: A Cohort Study

ObjectiveAlthough Caesarean section (CS) is protective for brachial plexus birth injury (BPBI), the incidence is not zero. A trial of labour with unfavourable intrauterine positioning is hypothesized to result in excessive force on the brachial plexus. The purpose of this study was to determine the risk of BPBI in emergent CS versus elective CS. MethodsThis was a retrospective cohort study. The authors used a nationwide demographic sample of all infants born in Canada from 2004 to 2012. BPBI diagnoses, risk factors, and national incidence data were obtained from the Canadian Institute for Health Information Discharge Abstract Database and Hospital Morbidity Database. The primary outcome was risk of BPBI in emergent CS versus elective CS. ResultsBPBI incidence was 1.24 per 1000 live births. Known biases may have underestimated the incidence. CS (elective and emergent) was protective for BPBI as compared with vaginal delivery (odds ratio [OR] 0.15; 95% confidence interval [CI] 0.13–0.18, P < 0.0001). Emergent CS was a moderately strong risk factor for BPBI versus elective CS (OR 3.14; 95% CI 1.79–5.10, P = 0.0001). ConclusionEmergent CS is a moderate risk factor for BPBI compared with elective CS. Intrauterine positioning with a trial of labour may provide an antenatal etiology in these distinct cases.

Six-month expulsion of postplacental copper intrauterine devices placed after vaginal delivery

Immediate placement of an intrauterine device after vaginal delivery is safe and convenient, but longitudinal data describing clinical outcomes have been limited. We sought to determine the proportion of TCu380A (copper) intrauterine devices expelled, partially expelled, malpositioned, and retained, as well as contraceptive use by 6 months postpartum, and determine risk factors for expulsion and partial expulsion. In this prospective, observational study, women who received a postplacental TCu380A intrauterine device at vaginal delivery were enrolled postpartum. Participants returned for clinical follow-up at 6weeks, and for a research visit with a pelvic exam and ultrasound at 6months. We recorded intrauterine device outcomes and 6-month contraceptive use. Partial expulsion was defined as an intrauterine device protruding from the external cervical os, or a transvaginal ultrasound showing the distal end of the intrauterine device below the internal os of the cervix. Multinomial logistic regression models identified risk factors associated with expulsion and partial expulsion by 6 months. The area under the receiver operating characteristics curve was used to assess the ability of a string check to predict the correct placement of a postplacental intrauterine device. The primary outcome was the proportion of intrauterine devices expelled at 6 months. We enrolled 200 women. Of 162 participants with follow-up data at 6 months, 13 (8.0%; 95% confidence interval, 4.7-13.4%) experienced complete expulsion and 26 (16.0%; 95% confidence interval, 11.1-22.6%) partial expulsion. Of 25 malpositioned intrauterine devices (15.4%; 95% confidence interval, 10.2-21.9%), 14 were not at the fundus (8.6%; 95% confidence interval, 5.2-14.1%) and 11 were rotated within the uterus (6.8%; 95% confidence interval, 3.8-11.9%). Multinomial logistic regression modeling indicated that higher parity (odds ratio, 2.05; 95% confidence interval, 1.21-3.50; P= .008) was associated with expulsion. Provider specialty (obstetrics vs family medicine; odds ratio, 5.31; 95% confidence interval, 1.20-23.59; P= .03) and gestational weight gain (normal vs excess; odds ratio, 9.12; 95% confidence interval, 1.90-43.82; P= .004) were associated with partial expulsion. Long-acting reversible contraceptive method use at 6 months was 80.9% (95% confidence interval, 74.0-86.6%). At 6 weeks postpartum, 35 of 149 (23.5%; 95% confidence interval, 16.9-31.1%) participants had no intrauterine device strings visible. Sensitivity of a string check to detect an incorrectly positioned intrauterine device was 36.2%, and specificity of the string check to predict a correctly positioned intrauterine device was 84.5%. This corresponds to an area under the receiver operating characteristics curve of 0.5. This prospective assessment of postplacental TCu380A intrauterine device placement, with ultrasound to confirm device position, finds a complete intrauterine device expulsion proportion of 8.0% at 6 months. The association of increasing parity with expulsion is consistent with prior research. The clinical significance of covariates associated with partial expulsion (provider specialty and gestational weight gain) is unclear. Due to the observational study design, any associations cannot imply causality. The proportion of partially expelled and malpositioned intrauterine devices was high, and the area under the receiver operating characteristics curve of 0.5 indicates that a string check is a poor test for assessing device position. Women considering a postplacental intrauterine device should be counseled about the risk of position abnormalities, as well as the possibility of nonvisible strings, which may complicate clinical follow-up. The clinical significance of intrauterine device position abnormalities is unknown; future research should evaluate the influence of malposition and partial expulsion on contraceptive effectiveness and side effects.

Ultrasound Guided Tandem Insertion: Improving Toxicity and Precision of Brachytherapy Applicator Placement in Cervical Cancer

To evaluate the benefit of intraoperative ultrasound (IOUS) guidance during intracavitary brachytherapy (ICBT) applicator insertion for the treatment of cervical cancer. Fifty-eight patients with cervical cancer were treated with ICBT at our institution between 1/1/13 and 12/31/16. Patients underwent 2 intraoperative insertions under general anesthesia and were treated using 7 Gy x 4 fractionation. Prior to 2015, IOUS was rarely used to guide tandem insertion. Upon root cause analysis (RCA), on 1/7/15 our institution initiated a policy requiring IOUS guidance for tandem insertions. We retrospectively reviewed clinical data to evaluate rates of intraoperative complications before and after mandating routine IOUS. Complications included uterine perforation and malpositioned applicator. Survival was estimated using the Kaplan Meier method and categorical comparisons were completed using Fisher’s test. One hundred thirty-seven tandem insertions were performed. The 4-yr overall complication rate was 7.4% (7 uterine perforations, 1 vaginal ulceration and 1 malpositioned split ring). Among patients with intraoperative complications, age ranged from 30-74 yrs, tumor size ranged from 1.6-7.2cm, and FIGO Stages included IB (22%), II (33%), III (44%). Prior to implementation of IOUS guidance, 10.1% (7 of 69) of insertions resulted in complications. After 1/7/2015, the complication rate dropped to 4.4% (3 of 68). The number of patients experiencing intraoperative complications was reduced from 25.0% (7 of 27) to 6.5% (2 of 21) of patients, a 74% relative reduction in risk (p = 0.046). At median follow up 11.2 months, overall survival and progression-free survival for these patients were 63.5% and 52% respectively. Among patients with perforation, 4 of 7 patients were treated with post-operative antibiotics. Four were observed 24 hr before discharge, 3 were discharged same day. The location of perforation varied–3 posterior, 2 anterior, and 2 through the fundus. Of note, 3 of 4 patients with highly anteverted uteri had posterior perforations. Six patients returned for reinsertion after 1 week, while one was observed and then underwent reinsertion after 24 hrs. All patients with perforation remained asymptomatic and stable. None developed fever, bleeding, abdominal pain, or vascular, urinary or bowel complications. Of the 9 patients with intraoperative complications, 8 successfully completed treatment on the 2ndattempt. Following incident RCA and implementation of routine IOUS to guide tandem placement, we noted a significant reduction in intraoperative complications. IOUS likely facilitated sounding and intrauterine positioning of the tandem. Eight of 9 patients who experienced complications successfully completed treatment, and none developed negative postoperative clinical sequelae.

Comparison of Clinical Findings of Congenital Muscular Torticollis Between Patients With and Without Sternocleidomastoid Lesions as Determined by Ultrasonography.

To compare clinical findings for patients with congenital muscular torticollis (CMT) between those with and without a sternocleidomastoid (SCM) lesion. Medical records of 182 patients with CMT were retrospectively reviewed and the patients were divided into SCM lesion and nonlesion groups by ultrasonographic results. Intrauterine position, age, duration of therapy, rotation/tilting side, and the passive range of motion and angle of the neck were compared. There were 74 SCM lesion and 108 nonlesion cases. The mean age at the first visit was 55.3 days in the SCM lesion group and 146.6 days in the nonlesion group. The mean therapy time in the nonlesion group was 66.5 days, significantly shorter than for the SCM lesion group (117.5 d). Tilting and rotation of the head in the same direction was observed only in the nonlesion group (n=9, 8.3%). Rotational limitation of the affected muscle side was 22.6 degree in the SCM lesion and 3.6 degree in the nonlesion group, and the tilting limitation was 19.2 degree in the SCM lesion and 10.4 degree in the nonlesion group. The nonlesion group had a better prognosis with shorter treatment duration. This group was more limited in head tilting than in head rotation, and the pattern of head rotation/tilting in the same direction was observed only in this group. These findings suggest that pathophysiological mechanisms and clinical characteristics may differ between CMT patients with and without SCM lesions. Level II-prognostic studies, retrospective study.

The phenotypic correlates and quantitative genetics of masculinization in the rodent, Octodon degus.

This corrects the article DOI: 10.1038/hdy.2017.20.

Paternal Care in Biparental Rodents: Intra- and Inter-individual Variation.

Parental care by fathers, although rare among mmmals, can be essential for the survival and normal development of offspring in biparental species. A growing body of research on biparental rodents has identified several developmental and experiential influences on paternal responsiveness. Some of these factors, such as pubertal maturation, interactions with pups, and cues from a pregnant mate, contribute to pronounced changes in paternal responsiveness across the course of the lifetime in individual males. Others, particularly intrauterine position during gestation and parental care received during postnatal development, can have long-term effects on paternal behavior and contribute to stable differences among individuals within a species. Focusing on five well-studied, biparental rodent species, we review the developmental and experiential factors that have been shown to influence paternal responsiveness, and consider their roles in generating both intra- and inter-individual variation. We also review hormones and neuropeptides that have been shown to modulate paternal care and discuss their potential contributions to behavioral differences within and between males. Finally, we discuss the possibility that vasopressinergic and possibly oxytocinergic signaling within the brain, modulated by gonadal steroid hormones, may represent the "final common pathway" mediating effects of developmental and experiential variables on intra- and inter-individual variation in paternal care.

The phenotypic correlates and quantitative genetics of masculinization in the rodent, Octodon degus.

In some mammals, female characteristics have been shown to depend, in part, on the intrauterine position during development of female fetuses relative to male fetuses. Females developing in close proximity to males show behavioral, physiological and life history characteristics that are masculinized. With the exception of one inconclusive study, nothing is known of the genetic basis of this phenomenon. In this paper, we reported an analysis of the quantitative genetic basis of masculinization, as indicated by the anogenital distance (AGD) at birth and weaning, in the rodent Octodon degus. Because AGD is related to weight, we included a genetic analysis of pup weight at birth and weaning. Pairwise correlations showed that AGD at birth varied negatively with litter size and parturition number but positively with weaning AGD, birth weight, dam AGD and percentage of males in the litter. AGD at weaning varied similarly except that it tended to vary positively with litter size. Genetic (co)variances of AGD at birth and weight at birth differed in females and males. In females, the best genetic model included substantial effects of direct additive, additive maternal and a negative additive genetic covariance between these two. In males, variances were small and there was difficulty in discriminating between additive maternal and common environmental variances. By weaning, genetic (co)variances had somewhat declined in weight and were not statistically significant in AGD in either sex. This paper showed the occurrence of both phenotypic and genetic components in masculinization with effects being greater in females.

Intrauterine embryo position is altered by obesity prior to implantation

Intrauterine embryo position is altered by obesity prior to implantation

Effect of Environmental and Behavioral Interventions on Pain Intensity in Preterm Infants for Heel Prick Blood Sampling in the Neonatal Intensive Care Unit.

Background:Recent researches suggest that preterm infants understand pain and stress. Because of the wide range of effects of pain on infants, the present study was conducted on the effect of environmental and behavioral interventions on pain due to heel-prick blood sampling in preterm infants.Materials and Methods:A clinical trial was conducted among 32 infants with gestational age of 32–37 weeks in the intervention and control groups. The effects of noise reduction by earplugs, light reduction by blindfolds, reduction of nursing manipulation, and creation of intrauterine position for neonates, 30 minutes before taking blood samples until 30 minutes after it, were measured during the intervention stage. Data were collected using the Neonatal Infant Pain Scale (NIPS) in 5 stages (before intervention, 2 minutes before sampling, during the sampling, and 5 minutes and 30 minutes after the sampling). The data were analyzed using analysis of variance (ANOVA) and paired t-test in SPSS software.Results:The paired t-test results showed no significant differences between the control and intervention stages in terms of pain scores at base time (P = 0.42) and 2 minutes before sampling (P = 0.12). However, at the sampling time (P = 0.0), and 5 minutes (P = 0.001) and 30 minutes after the sampling (P = 0.001), mean pain score in the intervention stage was significantly less than that in the control stage.Conclusions:Based on the findings, environmental and behavioral interventions reduced pain and facilitated heel-prick blood sampling in preterm infants.

TRIENNIAL REPRODUCTION SYMPOSIUM: Environmental programming of reproduction during fetal life: Effects of intrauterine position and the endocrine disrupting chemical bisphenol A.

During critical periods in fetal life, there is an increased vulnerability to perturbations in endocrine function due to environmental factors. Small shifts in concentrations of hormones that regulate the differentiation of organs, such as estradiol and testosterone, can have permanent effects on morphology, enzymatic activity, and hormone receptors in tissues as well as neurobehavioral effects. These changes can lead to effects throughout life, including impacting the risk for various diseases (referred to as the Developmental Origins of Adult Health and Disease hypothesis). The intrauterine position phenomenon concerns the consequence for fetuses of randomly implanting next to embryos of the same or opposite sex. An intrauterine position next to males vs. females results in small differences in serum testosterone and estradiol during fetal life that are associated with marked effects on life history (such as lifetime fecundity) in both males and females born in litters (mice, rats, gerbils, rabbits, and swine) as well as human twins. Research with mice subsequently demonstrated that a very small experimental change in fetal serum estradiol levels altered organogenesis and caused permanent changes in organ function. Taken together, these findings led to the hypothesis that environmental chemicals that mimic or antagonize hormone action (e.g., endocrine disrupting chemicals) could also be causing harm at very low exposures (the "low dose" hypothesis) within the range of exposure of humans, domesticated animals, and wildlife. There is now extensive evidence from experimental laboratory animals, sheep, and humans that fetal exposure to very low (presumably safe) doses of the endocrine disrupting chemical bisphenol A (BPA), which exhibits estrogenic activity, can cause permanent changes that can increase the risk of a wide array of diseases. The reasons that federal regulatory agencies are ignoring the massive literature showing adverse effects of BPA and other endocrine disrupting chemicals are discussed.

Gene changes may minimize masculinizing and defeminizing influences of exposure to male cotwins in female callitrichine primates.

BackgroundSexual differentiation in female mammals can be altered by the proximity of male littermates in utero, a phenomenon known as the intrauterine position effect (IUP). Among simian primates, callitrichines (marmosets and tamarins) are likely candidates for IUP, since they exhibit obligate dizygotic twinning and fetuses share extensive vascularization in utero. In this paper, we determined whether female reproductive parameters are altered by gestating with a male twin and evaluated changes in genes associated with anti-Müllerian and steroid hormones in twinning callitrichine primates.MethodsWe assessed the impact of gestation with male cotwins on reproductive performance and survivorship in female marmosets (Callithrix) and lion tamarins (Leontopithecus), contrasting measures for females gestated with one or more littermates (M+) or no male littermates (0M). We compared targeted coding regions for genes involved in steroidal and anti-Müllerian hormone mediation of sexual differentiation for representatives of twinning callitrichines (Callithrix, Saguinus, and Leontopithecus) with closely related New World primates that produce single births (Saimiri and Callimico).ResultsIUP effects in females were absent in female callitrichine primates: age at first ovulation, average litter size, and the proportion of stillborn infants, and lifetime survivorship did not differ between M+ and 0M females. We documented multiple nonsynonymous substitutions in genes associated with steroid synthesis, transport, and cellular action (SRD5A2, CYP19A1, SHBG, and AR) and with anti-Müllerian hormone (AMH and AMHR2) in callitrichines. In the only callitrichine to produce single infants (Callimico), two genes contained nonsynonymous substitutions relative to twinning callitrichines (CYP19A1 and AMRHR2); these substitutions were identical with nontwinning Saimiri and humans, suggesting a reversion to an ancestral sequence.ConclusionsIn spite of a shared placental vasculature with opposite-sex twins throughout embryonic and fetal development, female callitrichine primates gestated with a male cotwin exhibit no decrement in reproductive performance relative to females gestated with female cotwins. Hence, IUP effects on female reproduction in callitrichines are modest. We have identified mutations in candidate genes relevant for steroid hormone signaling and metabolism, and especially in AMH-related genes, that are likely to alter protein structure and function in the callitrichines. These mutations may confer protection for females from the masculinizing and defeminizing influences of gestating with a male cotwin.Electronic supplementary materialThe online version of this article (doi:10.1186/s13293-016-0081-y) contains supplementary material, which is available to authorized users.

Non-visualisation of strings after postplacental insertion of Copper-T 380A intrauterine device

AimTo assess the incidence of visible strings of intrauterine contraceptive devices (IUDs) after postplacental insertion following vaginal or caesarean delivery and to establish a management protocol of follow-up visits when...

Description of a Well Preserved Fetus of the European Eocene Equoid Eurohippus messelensis.

The early Middle Eocene locality of Grube Messel, near Darmstadt (Germany), is famous for its complete vertebrate skeletons. The degree of preservation of soft tissues, such as body silhouettes, internal organs and gut contents, is frequently remarkable. The present specimen was analyzed for remnants of the reproductive system. Classic anatomy and osteology and high-resolution micro-x-ray were applied to describe the fetus of the European Eocene equoid Eurohippus messelensis. Scanning electronic microscopy (SEM) was used for determination of soft tissue remnants. The fetus is the earliest and best-preserved fossil specimen of its kind. The postcranial fetal skeleton is almost complete and largely articulated, allowing the conclusion that the pregnant mare was in late gestation. The apparent intrauterine position of the fetus is normal for the phase of pregnancy. Death of mare and fetus were probably not related to problems associated with parturition. Soft tissue interpreted as the uteroplacenta and a broad uterine ligament are preserved due to bacterial activity and allow considerations on the evolutionary development of the structures.

A Proposed Classification for Intrauterine Device Position [228

A Proposed Classification for Intrauterine Device Position [228

Intrauterine position as a predictor of postnatal growth and survival in the rabbit

In mammals, body mass at birth is an important predictor of early postnatal growth and survival. Within litters, heavier young are more successful in competing for limited resources and show higher rates of growth and survival than their lighter sibs. In the present study, we investigated the contribution of two aspects of the intrauterine environment to within-litter differences in birth mass, growth and survival in the rabbit (Oryctolagus cuniculus): implantation site along the uterine horns and number of adjacent male fetuses. We used unilaterally ovariectomized mothers in order to infer relative sites of implantation from the birth order of pups from the single functional uterine horn. Pups from the extremities of the horn were significantly heavier at birth and weaning than their siblings from more central positions and had a higher probability of survival. The effect on body mass was still apparent 3 weeks after weaning in pups that had occupied positions at the ovarian end of the horn. The number of adjacent male fetuses did not affect individuals' growth or survival, and there were no differences between females and males. There were also no significant interactions between the different variables considered, indicating that the effects of implantation site on individuals' birth mass, growth and survival relative to littermates were independent of number of male neighbors, sex or litter size. Our study clearly demonstrates that in the rabbit, the site of implantation along the uterine horns is a major contributor to individual differences among littermates in early postnatal growth and survival.

Intrauterine position affects fetal weight and crown-rump length throughout gestation.

To investigate the effect of intrauterine positions on fetal growth throughout gestation, data from a total of 65 gilts (n = 784 fetuses) that were slaughtered at assigned days of gestation (d 43, 58, 73, 91, 101, and 108) on a project to evaluate fetal mineral deposition were used. Placenta units were removed from the uterus, and position, sex, weight, and crown-rump length (CRL) of each fetus were recorded. Fetuses were classified into 5 categories within a uterine horn for the absolute intrauterine position: the ovarian end (OE) of the uterine horn, next to the ovarian end (NOE), the middle (MD), next to the cervical end (NCE), and the cervical end (CE), and also classified for the relative fetal position with respect to the sex of adjacent fetuses. Fetuses at the OE and NOE of the uterine horn tended to be heavier (P = 0.06) and longer (P < 0.05) than those at the MD of the uterine horn at d 58 of gestation. Fetuses at the OE of the uterine horn were also heavier and longer than those at the MD and NCE of the uterine horn at d 101 and 108 of gestation (P < 0.05). Fetuses at the CE of the uterine horn were intermediate in weight and length. There were no major effects of adjacent fetal sex (fetuses surrounded by the opposite sexes) in weight or length. Male fetuses were heavier than female fetuses at d 43, 58, 73, and 108 of gestation (P < 0.05) and longer than female fetuses at d 58 (P = 0.06), 73 (P < 0.05), 101 (P = 0.07), and 108 (P < 0.05) of gestation. Fetal weight was highly correlated with CRL at all gestational ages (P < 0.01). These results indicate that 1) the absolute intrauterine position affects fetal growth more than the sex of the adjacent fetus in the uterine horn, 2) each end of the uterine horn (OE and CE) has heavier fetuses than the MD, and 3) male pigs grow faster than female pigs even before birth.